Use of respirators is required in a wide range of industrial environments including chemical, nuclear and biomedical facilities. Various types of respirators are known and currently employed. For example, respirator units including single or double respirator cartridges secured to a face mask or hood are commonly used. In some applications, respirator cartridges include high efficiency particulate air media (HEPA) certified by the National Institute for Occupational Safety and Health (NIOSH). These filters are capable of filtering out at least 99.97% of the particulates from a given test sample. HEPA media can be used alone in respirator cartridges or used in combination with a charcoal component which can react with and remove hazardous vapors and gases.
One form of respirator cartridge is shown in U.S. Pat. No. 4,714,486. This form of filter cartridge includes a radially pleated filter media which meets the high efficiency particulate air filter requirements of NIOSH. The radially pleated filter media enclosed in respirator cartridges of this type is secured within the cartridge structure by a perimeter seal of potting material. Commonly, the seal is formed using a rotational molding technique in which the sealant material is dispensed at or near the peripheral edge of the filter media where it cures in place while the respirator cartridge spins.
There are a number of problems associated with current rotational molding techniques. For example, the sealant material dispensed at the perimeter of the filter media has a tendency to dam-up between the respirator body and the edge of the filter media. Consequently, the sealant material flows inwardly over the filtering surface of the media thus reducing the overall efficiency and useful life of the respirator cartridge. Current in-place spin sealing methods are also not suitable for forming self supporting sealed filter elements. This precludes production of separate filter elements that can be assembled into new or existing respirator cartridges.
Therefore, a need exists for an improved respirator cartridge having a sealed filter media element and an improved rotational molding process for making respirator cartridges.